1. Field of the Invention
The present invention relates to a backlight module of a liquid crystal display, and more particularly to a backlight having a lens array to accelerate light diffusion and to achieve a thin module.
2. Description of Related Art
The liquid crystal display is not self-illuminating and so requires an additional lamp for providing a display function. Thus, the backlight module is one of the key components of the liquid crystal displays. As the size of the display panel increases, the edge-light type backlight module employing only one single lamp fails to satisfy the large-size panel with providing sufficient illumination. In this situation, most of the recent large-size panels adopt the direct-light type backlight module having a plurality of lamps. Some display parameters such as brightness, color and power consumption of the liquid crystal displays rely heavily on the backlight module. The direct-light type backlight module has multiple lamps mounted behind the display panel. Also, a diffuser plate is used so that light rays emitting from the respective lamps are uniformly projected onto the display panel. The quantity of the lamps is subject to the luminosity involved in different sized panels. In most cases, the direct-light type backlight module is adapted to the non-portable products such as desktop liquid crystal monitors and liquid crystal televisions. In particular, the liquid crystal television requires large size, wide view angle and high color saturation, and further requires a higher brightness than the liquid crystal monitor. Hence, more and more lamps are used.
However, the current display panels adopting the direct-light type backlight module cause the maximum brightness to occur directly above the lamps, resulting in non-uniform luminosity emitting from the backlight module, that is, dark and faded stripe problem. In general, the dark and faded stripe problem is solved by increasing the space between the lamp and the diffuser plate. This, however, increases the thickness of the backlight module, and does not conform to the current trend for a thin-type display panel. Accordingly, there is a strong need for the direct-light type backlight module to provide an improved module capable of speedily and uniformly diffusing light rays emitted from the lamps within a confined space. As shown in FIG. 1, U.S. patent application Ser. No. 10/330,593, entitled “Direct-lighting Type Backlight Unit”, discloses a prior art multiple concave lenses 110 disposed on a diffuser plate 100 to speedily diffuse illuminating rays 121 from lamps 120 corresponding to the concave lenses 110 and to achieve an reduced thickness of the backlight module. However, each of the lamps 120 has to be precisely aligned with the center axis of the corresponding concave lens 110 to obtain uniform light distribution, and no disclosure is provided as to how the multiple lamps 120 are precisely aligned with the center axis of the corresponding concave lenses 110. In addition, since the market requirement of liquid crystal displays is towards being larger and larger, fabrication of a single large-size diffuser plate having a plurality of concave lenses 110 after injection molding will cause a shrinkage problem. Shrinkage of the large-size diffuser plate will cause remarkable changes in the dimensions of the plate and misalignment of the lamps 120 respectively with the center axis of the concave lenses 110. Hence, it is not easy to fabricate a single large-size diffuser plate having multiple concave lenses aligned with the corresponding lamps and stable quality. In practice, it is necessary to adjust the modes for fabrication, accompanied by complex processes and labor-intensive operations. Even so, the uniform illumination effect is rarely achieved.
Therefore, it is desirable to provide an improved lens-arrayed backlight module and liquid crystal display device to mitigate and/or obviate the aforementioned problems.